Some time ago, Svetitsky and Yaffe have argued that -if the deconfinement phase transition of a (d + 1)-dimensional Yang-Mills theory with gauge group G is second order -it should be in the universality class of a d-dimensional spin model symmetric under the center of G. For d = 3 these arguments have been confirmed numerically only in the SU(2) case with center Z Z(2), simply because all SU(N) Yang-Mills theories with N ≥ 3 seem to have non-universal first order phase transitions. The symplectic groups Sp(N) also have the center Z Z(2) and provide another extension of SU(2) = Sp(1) to general N. Using lattice simulations, we find that the deconfinement phase transition of Sp(2) Yang-Mills theory is first order in 3 + 1 dimensions, while in 2 + 1 dimensions stronger fluctuations induce a second order transition. In agreement with the Svetitsky-Yaffe conjecture, for (2 + 1)-d Sp(2) Yang-Mills theory we find the universal critical behavior of the 2-d Ising model. For Sp(3) Yang-Mills theory the transition is first order both in * on leave from MIT